3-methoxy-2, 6-dichlorophenylacetates



Bfildfilih Patented Bee. l2, l fil 3,ll3,t'l56 3=METH9XY=2,-DTCPZLGRGPHER ZIJA'QETATES Sidney B. tlhicago, TEL, assignor to Velsicol C" ration, Qhieago, Ill., a corporation or Ennis No Get.

12 filaims.

13, 1953, 5e11, No. '2 66,66ll (Cl. 269-473) OCHs will hereinafter be referred to as compound I. This chemical compound and its derivatives as cited above have marked activity as herbicides useful for the control of undesirable plant life.

Compound I can he prepared readily, for example, from the known compound 2,6-dichloro-m-cresol. The free hydroxy group in the cresol is first protected against reaction in subsequent steps in the synthesis by the addition of such groups as CO H, COR (where R=allryl), -PO l-I and the like. Thus the protective group can be made the acetyl radical by treating 2,6-dichloro-m-cresol with acetic anhydride in the presence of a few drops of sulfuric acid as catalyst, or the protective group can be made the phosphate radical by treating the cresol with POCl With the hydroxy group suitably protected, the 2,6-dichloro-m-cresol is chlorinated to introduce a single chlorine atom into the methyl group. The chlorination, which can be effected with gaseous chlorine, is catalyzed by light and free radical initiators and is continued until a slight excess of chlorine over the amount theoretically required for the addition or" one gram atom of chlorine into each mole of starting compound has been added. The chlorination can be carried out merely by passing chlorine into the molten starting material, but inert solvents or diluents such as carbon tetrachloride can also be used at temperatures up to about reflux temperature.

The 2,4-dichloro-3-chloromethylphenyl acetate is then placed in a suitable solvent or diluent such as methanol and is heated with an aqueous solution of a cyanide such as sodium cyanide to convert it to the corresponding 2,4- dichloro-3-cyanomethylphenyl acetate. The cyano compound is hydrolyzed with strong sulfuric acid, for example, in aqueous medium to give the free 2,6-dichloro- B-hydroxyphenylacetic acid. The acid is converted to its alkali metal salt with an alkali metal hydroxide such as sodium or potassium hydroxide, and the salt is refluxed in aqueous solution with an excess of dimethyl sulfate. The reaction mixture is refluxed with additional a hall metal hydroxide to hydrolyze any carboxylic acid ester which may have formed, cooled, and acidified with a mineral acid such as hydrochloric acid. The precipitated acid can be filtered oft" and dried to give a product which is suitable for many herbicidal uses as such. However, if desired, it can be purified by crystallization from a suitable solvent.

The anhydride of compound I is prepared by the removal of one molecule of Water fromtwo molecules of compound I as the free acid. In practice, it is convenient to prepare the anhydride by the acylation of the free carboxylic acid by its acid halide in the presence of a strong acylating agent such as pyridine. Thus a mixture of dry pyridine and dry benzene are treated with 1 mole of the acid chloride of compound I. The slightly exothermic reaction proceeds with the formation of an intermediate pyridinium salt. One mole of compound I as the free acid is then added, the precipitate of pyridine hydrochloride is removed, and the anhydride of compound I is isolated by removal of the benzene.

The acid halide of compound I required in the above and other syntheses is prepared by the reaction of the free acid with a phosphorus trihalide in the conventional manner. Thus the treatment of compound I with phosphorus trichloride until the reaction ceases produces the acid chloride of compound 1.

Compounds which are salts, esters, or amides of compound I can be prepared readily from the free acid. Thus treatment of the free acid with ammonium hydroxide gives a product which is the salt ammonium 3-methoxy- 2,6-dichlorophenylacetate. Similarly, an alkali metal salt of compound I can be made by the treatment of the free acid with bases, such as the hydroxides, of alkali metals. Treatment of the acid with sodium hydroxide thus gives the salt sodium 3-methoxy-2,6-dichlorophenylacetate as the product, while the use of potassium hydroxide gives the salt potassium 3-methoxy-Z,6-dichlorophenylacetate.

Amine salts of compound I are prepared by the addition of the free acid to various amines. Typical amines which can be used to prepare such amine salts are dimethylamine, trimethylamine, triethylamine, diethanolamine, triethanolamine, isopropylamine, morpholine, and the like. The resulting products are, respectively, the dimethylamine, trirnethylamine, triethylamine, diethanolamine, triethanolamine, isopropylamine, and morpholine salts of 3-methoxy-2,6-dichlorophenylacetic acid.

Esters of compound I are prepared by the condensation of the acid with various alcohols. Thus the com densation of methyl alcohol with compound I gives the desired ester, methyl 3-methoxy-.Z,6-dichlorophenylacetate. Other typical alcohols which can be used are propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, amyl, hexyl, heptyl, octyl, nonyl, decyl and the like. The products are the corresponding allryl esters of 3-methoxy-2,6- dichlorophenylacetic acid. Although such complex esters as those prepared by the esterification of compound I with butoxyethanol, propylene glycol butyl ether, and the like are useful products in accordance with this invention, preferred esters are those in which the esteritying group is an unsubstituted alkyl group which contains from 1 to 10 carbon atoms. The condensation of the acid with the alcohol is carried out suitably in an inert solvent such as an aromatic hydrocarbon and in the presence of a few percent by weight of an acid catalyst such as p-toluenesulfonic acid. The Water which forms during the esterification reaction can be removed continuously in many cases from the reaction mixture by distillation as it forms, and its volume can be measured to determine when the esterification is complete. The ester is then isolated by distillation of the inert solvent.

Amides of compound I can be prepared conveniently by the reaction of the acid halide of compound I with ammonia or various amines. The reaction can be carried out in an inert solvent such as ether or benzene. Preferably two moles of the amine are used for each mole of the acid halide employed, since the hydrogen halide released during the reaction is taken up by some of the free amine which remains. The simplest amide, 3-methoxy-2,6-dichlorophenylacetamide, can be prepared by the reaction of the acid chloride of compound I with ammonia, either as the free gas or as an aqueous solution. This amide can also be prepared by hydrolysis of the corresponding nitrile. Substituted amides are prepared by the reaction of the acid halide of compound I with amines such as any of the primary or secondary amines sugested above for the preparation of the amine salts of compound 1. Thus, for example, the reaction of the acid chloride of compound I with methylamine, butylamine, decylamine, or diethylamine gives the N-methyl-, N-butyl-, N-decyl-, or N,N-diethyl-3-methoxy-2,6-dichlorophenylacetamides, respectively. While more complex amines such as the aromatic amines can be used as the amine reactant to give desirable products, which are specifically named as anilides, preferred amine reactants are alkylamines containing up to 10 carbon atoms.

For practical use as herbicides, the compounds of this invention are formulated with inert carriers to obtain proper concentrations and to facilitate handling. For example, these compounds can be formulated into dusts by combining them with such inert substances as talc or clays. The alkali metal salts of compound I are particularly suited to such dust formulations, and dusts containing from 5 to 25 percent by weight of active compound are convenient for use in the field. The compounds of this invention, however, are preferably applied as sprays. These can be made as simple solutions by dissolving the compounds in organic solvents such as xylene, kerosene, or the methylated naphthalenes. The esters of compound I, which ordinarily are liquids at room temperature, are particularly suited to formulation by this method. The amine salts of compound I often show good solubility in water and can be used directly as aqueous solutions.

The compounds of this invention can also be emulsified or suspended in water by the addition of emulsifiers and wetting agents. The formulations of these active herbicidal compounds are either applied directly to the plants to be controlled, or the soil in which the plants are growing can be treated. Substances such as other pesticides, stabilizers, activators, synergists, spreaders and adhesives can be added to the formulations if desired. There is no significant difference in effect from the amount of water or organic solvent for diluting these herbicides, providing the same amount of chemical is distributed evenly over a given area. Such distribution can be obtained, for example, with low-pressure, lowvolume sprays at the rate of about gallons of spray per acre.

In applying the herbicidal compounds, consideration must be given to the nature and stage of growth of the crop, the species of weeds present, the stage of growth of the weeds, environmental factors influencing the rate and vigor of the weed growth, weather conditions at the time of application and immediately following, and the dosage to be applied to a given area. Weeds are most susceptible when they are small and growing rapidly. Early application, therefore, results in better control with less chemical and increased yields because of the early destruction of the competing weeds. The larger and older the weeds the higher the concentration needed to kill them. Summer annuals such as lambs-quarters, pigweeds, cocklebur, and sunflower should be sprayed when they are less than 4 inches higher. Winter annuals such as various mustards, fan-weed, yellow star-thistle, and wild radish are most easily killed while they are still in the rosette stage. Usually weeds growing rapidly under optimum conditions are relatively susceptible, whereas those growing under adverse conditions tend to be resistant to the herbicide sprays.

The eifectiveness of the compounds of this invention in small quantities makes them economically sound for weed control on large areas, with a great saving in labor and cost, in addition to corresponding crop increases. These compounds are particularly valuable in weed control beacuse they are harmful to many weeds but harmless or relatively harmless to some cultivated crops. Minute quantities in contact with plant tissues may be absorbed and translocated to all parts of the plant, causing striking changes in the form and functions and often resulting in their death. The actual amount of compound to be used depends on a variety of factors but is influenced primarily by the species of undesirable plant to be controlled. Thus while fractions of a pound of actual compound I or its equivalent of an ester, salt, amide, or the anhydride of compound I are often sufficient for post-emergence weed control on an acre of corn, seed flax, perennial grass seed crops, pastures or grazing areas (without legumes), wheat, and the like, the particular species of weeds encountered in evergreen and deciduous dormant nursery stock, nursery conifers, waste areas, woody brush, and the like may require the use of one or more pounds of compound I or its derivatives per acre for good control. Dosage adjustments with the low-volume, low-pressure applications suggested can be made by changing the nozzle size, nozzle spacing, pressure, or traveling rate of the spray equipment.

The manner in which the herbicidal compounds of this invention can be prepared and utilized is illustrated in the following examples:

' EXAMPLE 1 Preparation of 2,6-dichl0r0-3-hydr0xyphenylacetic acid 2,6-dichloro-m-cresol (100 g.; 0.56 mole), which can be obtained, for example, as described by Huston and Chen in the Journal of the American Chemical Society, vol. 55, p. 4217 (1933), is placed with acetic anhydride g.; 0.78 mole) and a few drops of concentrated sulfuric acid in a 250 ml., 3-necked, round-bottomed flask fitted with a mechanical stirrer, reflux condenser, and internal thermometer. The mixture is stirred and heated at C. for 4 hrs. and is then allowed to stand at room temperature overnight. The mixture is then poured slowly with stirring into a solution of g. sodium bicarbonate in 700 ml. of water and is then extracted with two 500 ml. portions of ether. The ether extracts are combined, washed with two 250 ml. portions of 10% sodium hydroxide and then with two 250 ml. portions of water, dried over magnesium sulfate, and filtered. The other is distilled off, and the residue is distilled in vacuo to give 2,4-dichloro-3-methylphenyl acetate. The acetate (108 g.; 0.49 mole) is placed in a 250 ml., 3- necked, round-bottomed flask fitted with a mechanical stirrer, reflux condenser, internal thermometer, and gas inlet tube. The acetate is heated and stirred at 180 C. while gaseous chlorine is passed into the mixture until 15.6 g. of chlorine has ben introduced. The reaction mixture is then cooled to give the desired 2,4-dichloro- 3-chloromethylphenyl acetate.

Sodium cyanide (77 g.; 1.57 moles), 110 ml. water, ml. methanol are placed in a 1-liter, 3-necked, roundbottomed flask fitted with a mechanical stirrer and reflux condenser. The mixture is stirred and heated to reflux, and 2,4-dichloro-3-chloromethylphenyl acetate (0.90 mole) is added slowly. The mixture is stirred and refluxed for 3 hours, cooled, and extracted with three 300 ml. portions of ether. The combined ether extracts are washed with water, dried over magnesium sulfate, and filtered. Distillation of the ether gives a residue of 2,4- dichloro-3-cyanomethylphenyl acetate. A portion of the cyano compound (0.80 mole) is stirred and refluxed for 6 hours with 900 ml. of water and 750 ml. of concentrated sulfuric acid in a 3-liter, 3-necked, round-bottomed flask fitted with a reflux condenser and a mechanical stirrer. The mixture is then cooled and poured slowly with stirring into 3 liters of ice water. The solid is filtered, washed with cold water, pressed dry, and dried completely in a vacuum oven to give 2,6-dichloro-3-hydroxyphenylacetic acid.

EXAMPLE 2 Preparation of 3-meth0xy-2,6-dichlorophenylacetic acid (compound I) (B totned flask fitted with a mechanical stirrer, reflux condenser, dropping funnel, and internal thermometer. The solution is cooled to 20 C., and dimethyl sulfate (219 g.; 1.74 moies) is added to the vigorously stirred solution. Themixture is stirred for 20 minutes while the temperature is maintained below 35 C. by ice-cooling. Another portion of dimethyl sulfate (139 g.) is added, and the mixture is stirred for 10 minutes while the temperature is maintained below 45 C. The mixture is then refluxed for 2 hours, treated with a solution of 69.2 g. (1.74 moles) of sodium hydroxide in 250 ml. of water, and refluxed for an additional 2'hours. The cooled reaction mixture is then acidified to Congo red with hydrochloric acid. ,The precipitated solid is filtered, dissolved in ether, and dried over magnesium sulfate. The ether solution is filtered, and the ether is distilled oif to give a residue of the desired compound I. 9

EXAMPLE 3 Preparation of the sodium salt of compound I Compound 1 (0.5 mole) is dissolved in 500 cc. of methanol and treated with a solution of sodium hydroxide (20 g.; 0.5 mole) in 100 cc. of methanol. The methanol is removed by distillation in vacuo on the steam bath, and the solid residue is slurried with 100 cc. of cold, dry ether, filtered, pressed dry, and dried completely in a vacuum oven to give the desired sodium salt of compound I. EXAMPLE 4 Preparation of the ammonium salt of compound I Treatment of compound I (0.5 mole) in 500 cc. of methanol with 34 cc. of commercial concentrated am monium hydroxide according to the method given in the previous example gives the, desired ammonium salt of compound I.

EXAMPLE 5 Preparation of the dimethylamine salt of compound 1 Compound I (0.5 mole) is dissolved in 500 cc. of dry ether and treated with dimethylamine (22.5 g.; 0.5 mole). The solid which separates is filtered, washed twice with 100 cc. portions of cold ether, filtered, pressed dry, and dried completely in a vacuum oven to give the desired dimethylamine salt of compound I.

EXAMPLE 6 Preparation of the diethanolamine salt of compound I In the manner described in the previous example, compound I (0.5 mole) is treated with diethanolamine (52.5 g.; 0.5 mole) in 500 cc. of dry ether. The product which is isolated is the diethanolamine salt of compound I.

EXAMPLE 7 Preparation of the morpholine salt of compound I Compound I (0.5 mole) is treated with morpholine (43.5 g.; 0.5 molelin 500 cc. of ether, and the product is worked up as de scribed for the preparation of the dimethylamine salt to ive the desired morpholine salt of compound 1.

EXAMPLE 8 Preparation of the ethyl ester of compound I Compound I (0.5 mole), ethyl alcohol (23 g.; 0.5 mole), and 3.0 g. of p-toluenesulfonic acid are dissolved in 500 ml. of benzene, and the solution is placed in a 1-liter, round-bottomed flask fitted with a reflux condenser and a calibrated Dean-Stark tube. The solution is heated at reflux temperature until 9 cc. of water have been collected in the Dean-Stark tube. The cooled reaction mixture is then extracted twice with 50-cc. portions of 10% sodium carbonate solution, and filtered. The benzene is distilled off in vacuo on the steam bath, and the residue is then distilled in vacuo to give the desired ethyl ester of compound I.

EXAMPLE 9 Preparation of the decyl ester of compound I In the manner and apparatus described in the previous The reaction of compound I (0.5 mole) and n-butyl alcohol (37 g.; 0.5 mole) by the method described above for the preparation of the ethyl ester is used to prepare the n-butyl ester of compound I.

EXAMPLE 11 Preparation of the acid chloride of compound I Compound I (1 mole) is placed with 500 cc. of dry benzene in a 2-liter, 3-necked,round-bottomed flask fitted with a mechanical stirrer, reflux condenser (calcium chloride tube), and dropping funnel. Phosphorus tr-ichloride (123 g.; 0.9 mole) is added slowly dropwise with vigorous stirring while the reaction flask is cooled With cold Water if necessary to control the reaction. When all the PCl has been added and the evolution of hydrogen chloride has ceased, the reaction mixture is then transferred to distillation apparatus, and the solvent is distilled oif. The residue is then distilled in vacuo to give the desired acid chloride of compound 1.

EXAMPLE 12 Preparation. of the amide of compound I One mole of the acid chloride of compound I is placed with 500 cc. of dry benzene in a l-liter, 3-necked flask fitted with a reflux condenser, mechanical stirrer, and a gas inlet tube having a sparger ti The mixture is stirred while dry ammonia gas is passed into the mixture for several hours. When the ammonia gas is no longer taken up, the precipitated salt is filtered oil? and extracted twice with ml. portions of ether. The ether extracts and benzene filtrate are dried over magnesium sulfate and filtered, and the solvents are distilled oil to give the desired amide, of compound I.

EXAMPLE 13 Preparation of the N-n-decylamide of compound I One mole of the acid chloride of compound I and 500 ml. of dry benzene are placed in a 2-liter, 3-necked, roundbottom flask fitted with a mechanical stirrer, reflux condenser, internal thermometer, and dropping funnel. n-Decylarnine (314 g.; 2.0 moles) in 250 m1. benzene is added dropwise with vigorous stirring. When all the amine has been added, the reaction mixture is refluxed for 2; hours and cooled, after which the precipitated salt is filtered off and extracted with two 100 ml. portions of ether. The ether extracts and benzene filtrate are dried over magnesium sulfate and filtered. Distillation of the solvents gives the desired N-n-decylamide of compound 1.

EXAMPLE 14 Preparation of the N,N-diethylamide of compound I One mole of the acid chloride of compound I is treated with diethylamine (146 g.; 2.0 moles) in the manner and apparatus described in the previous example to give the N,N-diethylamide of compound I.

'7' EXAMPLE 15 Preparation of the anhydria'e of compound 1 Dry pyridine (158 g.; 2.0 moles) and 1 liter of dry benzene are placed in a 2-liter, 3-necked round-bottom flask fitted with a dropping funnel, mechanical stirrer, reflux condenser, and internal thermometer. One mole of the acid chloride of compound I, which is prepared as described in a previous example, is added rapidly with stirring to the reaction mixture. Compound I (1 mole) is then added in portions over a period of about minutes with rapid stirring. The pyridine hydrochloride which precipitates is filtered off, and the benzene is distilled from the filtrate in vacuo. The residue contains the desired anhydride of compound I, which can be purified by crystallization from a suitable solvent.

EXAMPLE 16 Preparation of an emulsifiable concentrate of compound I The following concentrate is prepared by mixing the ingredients intimately in the given percentage proportions by Weight:

Percent Compound I 25 Antarox A-400 40 Methanol 35 Antarox A-400 is the trade name under which a nonionic detergent of the aromatic polyethylene glycol ether type is sold. The above concentric is diluted with water to the desired concentration for use.

EXAMPLE 17 Preparation of an emulsifiable concentrate of the n-butyl ester of compound I The following ingredients are mixed thoroughly in the given percentage proportions by weight:

Triton X400 is the trade name under which an emulsifier of the alkyl aryl polyether alcohol type is sold. The above concentrate is diluted with water to the desired concentration for use.

EXAMPLE 18 Preparation of a dust from the sodium salt of compound I The sodium salt of compound I (10% by weight) and talc (90% by Weight) are combined and ground to the desired particle size in a mechanical grinder-blender.

The herbicidal activity of chemical compounds is often demonstrated by the ability of the chemicals to kill or arrest the growth of tomato plants. The tomato plant is readily grown and maintained under uniform conditions for experimental purposes in greenhouses, and its response to chemicals is very similar to that observed for a Wide variety of economically important species of undesirable plant life in the field.

The herbicidal activity of the compounds of this invention, for example, can be demonstrated in greenhouse experiments on young potted tomato plants (Bonny Best variety). The compounds are formulated into 10 percent wettable powders and are dispersed in water at a concentration of 2,000 parts per million actual chemical.

Ten milliliters of an aliquot portion of the dispersion is added to the soil surface of the tomato plants, approximately 5 to 7 inches tall. In order to avoid undue concentration or accumulation of the chemical in any given area, 5 holes the size of a pencil and about 1 inch deep are punched in the soil surface around the shoot, and the 10 milliliter application is divided equally among the 5 holes. Three plants are used for each application. The treated plants are held under greenhouse conditions for 7 days, provided with subterranean watering, and observed for responseto treatment. The results indicate a high order of herbicidal toxicity of the compounds of this invention.

I claim as my invention:

1. A compound selected from the group consisting of 3-methoxy-2,6-dichlorophenylacetic acid, its anhydride, its alkali metal salts, its ammonium salt, its morpholine salt, its alkyl amine salts in which the amine component is an unsubstituted alkyl amine of up to six carbon atoms, its alkanol amine salts in which the amine component is an unsubstituted alkanol amine of up to six carbon atoms, its esters in which the esterifying group is an unsubstituted alkyl group of from one to ten carbon atoms, its butoxyethanol ester, its unsubstituted amide, and its alkyl amides in which the amine component is an unsubstituted alkyl amine of up to ten carbon atoms.

2. An alkali metal salt of 3-methoxy-2,6-dich1orophenylacetic acid.

3. An alkyl amine salt of 3-methoxy-2,6-dichlorophenylacetic acid in which the amine component is an unsubstituted alkyl amine of up to six carbon atoms.

4. An ester of 3-methoxy-2,6-dichlorophenylacetic acid, in which the esteritying group is an unsubstituted alkyl group of from one to ten carbon atoms.

5. An alkyl amide of 3-methoxy-2,6-dichlorophenylacetic acid in which the amine component is an unsubstituted alkyl amine of up to ten carbon atoms.

6. An alkanol amine salt of 3-rnethoxy-2,6-dichlorophenylacetic acid in which the amine component is an unsubstituted alkanol amine of up to six carbon atoms.

7. The dimethylamine salt of 3-methoxy-2,6-dichlorophenylacetic acid.

8. 3-methoxy-Z,6-dichlorophenylacetic acid.

9. Sodium 3-methoxy-2,6-dichlorophenylacetate.

10. The diethanolamine salt of 3-methoxy-2,6-dichlorophenylacetic acid.

11. n-Butyl 3-methoxy-2,6dichlorophenylacetate.

12. Bis-(3-methoxy 2,6 dichlorophenylacetic) anhydride.

References Cited in the file of this patent UNITED STATES PATENTS 2,341,867 Hitchcock et al. Feb. 15, 1944 2,396,513 Jones Mar. 12, 1946 2,548,852 Archer Apr. 17, 1951 2,580,459 Papa et al. Jan. 1, 1952 2,633,418 Scott et al. Mar. 31, 1953 2,681,363 Schwenk et al. June 15, 1954 2,695,840 Leppla Nov. 30, 1954 OTHER REFERENCES Weintraub et al.: Bot. 6212., 113, 359, March (1952), 71-2.6.

Julia et al.: Bull. Soc. Chim. France, 640-3 (1953), 260-521A.

Bradsher et al.: I. Am. Chem. Soc., 79, 1468-9 (1957). 

1. A COMPOUND SELECTED FROM THE GROUP CONSISTING OF 3-METHOXY-2,6-DICHLOROPHENYLACETIC ACID, ITS ANHYDRIDE, ITS ALKALI METAL SALTS, ITS AMMONIUM SALT, ITS MORPHOLINE SALT, ITS ALKYL AMINE SALTS IN WHICH THE AMINE COMPONENT IS AN UNSUBSTITUTED ALKYL AMINE OF UP TO SIX CARBON ATOMS, ITS ALKANOL AMINE SALTS IN WHICH THE AMINE COMPONENT IS AN UNSUBSTITUTED ALKANOL AMINE OF UP TO SIX CARBON ATOMS, ITS ESTERS IN WHICH THE ESTERIFYING GROUP IS AN UNSUBSTITUTED ALKYL GROUP OF FROM ONE TO TEN CARBON ATOMS, ITS BUTOXYETHANOL ESTER, ITS UNSUBSTITUTED AMIDE, AND ITS ALKYL AMIDES IN WHICH THE AMINE COMPONENT IS AN UNSUBSTITUTED ALKYL AMINE OF UP TO TEN CARBON ATOMS.
 4. IN AN ESTER OF 3-METHOXY-2,6-DICHLOROPHENYLATIC ACID, IN WHICH THE ESTERIFYING GROUP IN AN UNSUBSTITUTED ALKYL GROUP OF FROM ONE TO TEN CARBON ATOMS. 